AMES, Iowa - A yearly festival near the Iowa State University campus turned riotous early Sunday when more than 1,000 people vandalized cars, broke storefront windows and tore down street lights, police said.

Officers broke up the crowd with tear gas and arrested about 30 people on charges ranging from disorderly conduct to assaulting a police officer, police said.

About 20 people received treatment for minor injuries at a hospital, mainly for skin and eye irritations.

There were no estimates of property damage Sunday afternoon, but police said the damage was "extensive."

Officers responded to a call around midnight that a group of people at the annual student-organized Veishea celebration was getting out of hand and arrived to find a crowd of several hundred people flowing into the street.